1. Field of the Invention
The present invention relates in general to mounting devices for mounting a power unit on a body of a motor vehicle, and particularly to mounting devices of a type which includes an inner member, an outer case surrounding the inner member and an elastomer block resiliently disposed between the inner member and the outer case. More specifically, the present invention is concerned with mounting devices of a fluid-filled type which has in the elastomer block a fluid-filled chamber for damping a vibration of the elastomeric member.
2. Description of the Prior Art
Hitherto, a so-called fluid-filled type mounting device has been proposed and put into a practical use for its marked vibration damping effect. The mounting device of this type comprises generally an outer cylindrical case secured to a vehicle body (or power unit), an inner cylindrical member received in the outer case and secured to the power unit (or vehicle body), an elastomer block resiliently disposed between the outer case and the inner member, and fluid chambers defined by the elastomer block and communicated through a flow restricting passage. In response to resilient deformation of the elastomer block due to vibration of the power unit, the fluid in one of the fluid chambers is forced to flow to the other through the flow restricting passage damping vibration of the elastomer block transmitted thereto from the power unit.
In order to clarify the task of the present invention, one of the mounting devices of this type hitherto proposed by the same applicants will be outlined with reference to FIGS. 6 and 7 of the accompanying drawings, which is disclosed in Japanese Patent Application 62-1429.
As shown in the drawings, the mounting device 1 comprises an outer cylindrical case 4, an inner cylindrical member 3, a cylindrical elastomer block 5 disposed between the outer case 4 and the inner member 3. A main fluid chamber 2 is defined in one side of the elastomer block 5, a first auxiliary fluid chamber 6a is defined at a diametrically opposed side of the main chamber 2, and a second auxiliary fluid chamber 6b is defined near the main fluid chamber 2, as shown.
Each of the auxiliary chambers 6a and 6b is partially defined by a diaphragm 7 whose spring constant is controllable independent of the elastomer block 5. The main fluid chamber 2 communicates with the first auxiliary fluid chamber 6a through flow restricting passages 8 and 8 each extending circularly around the elastomer block 5, and the main fluid chamber 2 communicates with the second auxiliary fluid chamber 6b through an orifice 9d. It has been revealed that the provision of the two auxiliary fluid chambers 6a and 6b provides the mounting device 1 with a vibration damping characteristic with which the shaking of the engine and the idling vibration of the same are both damped by a satisfied degree at the same time.
However, the mounting device 1 as described hereinabove has a very complicated construction. In fact, as is shown in the drawings, the main fluid chamber 2 is provided by tightly disposing a rectangular box structure 9 in a mouth portion of a blind bore formed in the elastomer block 5. Each of the flow restricting passages 8 and 8 comprises an opening 9a formed in the box structure 9, an orifice 9b or 9c formed in the box structure 9 and an elongate passsage 8a or 8b extending circularly around the elastomer block 5. The orifice 9d communicating the main fluid chamber 2 and the second auxiliary fluid chamber 6b is formed in the box structure 9 also.
A semicylindrical structure 8c which partially defines the elongate passages 8a and 8b is divided into two parts at the position where the box structure 9 is positioned. The first auxiliary fluid chamber 6a is defined by the diaphragm 7 and a part of the semicylindrical structure 8c, while the second auxiliary fluid chamber 6b is defined by the other diaphragm 7 and the box structure 9.
The second auxiliary fluid chamber 6b is communicated with the main fluid chamber 2 through the orifice 9d and the elongate passage 8b which turns about two times about the elastomer block 5. Accordingly, as is seen from FIG. 7, there is a need of providing the semicylindrical structure 8c with three grooves 8b, 8b and 8a.
As is known, complicated construction of the mounting device 1 induces not only increase in production cost but also increase in malfunction possibility.